release: v5.12.0 — "Auto-calibration" (B8b)

Version-sync for the B8b model→window auto-probe shipped in cf75249:
- plugin.json 5.11.0 -> 5.12.0
- README version badge + version-history row (1296 tests)
- CHANGELOG [5.12.0] entry

Scanner count stays 16, agents 7, commands 21. No new finding ID or scanner.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,42 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [5.12.0] - 2026-06-23
+
+### Summary
+"Auto-calibration" — completes the deferred half of B8. `--context-window auto` now **probes the
+configured model** and calibrates SKL/CML budgets to its real context window, instead of always
+falling back to the conservative advisory anchor. A 1M-tier host self-calibrates without the manual
+`--context-window 1000000`. No new finding ID or scanner (count stays **16**, agents **7**, commands
+**21**); the default and explicit `--context-window` paths are unchanged, so `--json`/`--raw` stay
+byte-stable and the frozen v5.0.0 + SC-5 snapshots are untouched. **1296** tests.
+
+### Added
+- **B8b — model→window auto-probe.** `lib/context-window.mjs` gains a pure `modelToContextWindow()`
+  that maps a configured model id/alias to its context window:
+  - the explicit `[1m]` tier tag wins (the running session model surfaces as e.g.
+    `claude-opus-4-8[1m]`);
+  - known 1M-tier families `LARGE_CONTEXT_MODEL_IDS` (`claude-fable-5`, `claude-opus-4-8`,
+    `claude-opus-4-7`, `claude-opus-4-6`, `claude-sonnet-4-6` — verified June 2026 against the
+    platform.claude.com models overview) match by substring, so dated (`-20260528`) and
+    provider-prefixed (`us.anthropic.…`) IDs resolve too;
+  - the short aliases `opus` / `sonnet` / `fable` / `opusplan` resolve to 1M.
+  - Models we cannot confirm (Haiku, older 200k-era IDs, unknown) return `null` — the caller then
+    keeps the conservative anchor rather than guess a relaxed budget.
+- **New IO helper `lib/active-model.mjs` `resolveActiveModel()`** reads the configured model the way
+  Claude Code resolves it: the shell `ANTHROPIC_MODEL` override first, otherwise the settings cascade
+  `model` field (user `~/.claude` → project `.claude` → project-local, local wins). Reads the cascade
+  files directly (like `isBundledSkillsDisabled`) and takes an injectable `env`, so it stays
+  deterministic and hermetic under the test HOME. Returns `null` when no model is pinned anywhere.
+
+### Changed
+- **`resolveContextWindow(arg, opts)` — the `auto` branch now probes.** It maps `opts.model` via
+  `modelToContextWindow()`: a recognized 1M-tier model calibrates to its window (source `auto-probed`,
+  **not** advisory); an unknown or unpinned model keeps the conservative 200k anchor and stays advisory
+  (source `auto-unresolved`, the pre-B8b `auto` behavior). `scan-orchestrator` resolves the active
+  model (only when the flag is `auto`) and threads it in; `posture` inherits this via `runAllScanners`.
+  The default (no flag) and explicit `--context-window <n>` paths ignore `opts.model` and are unchanged.
+
 ## [5.11.0] - 2026-06-23
 
 ### Summary